In a high-temperature, high-wear environment, such as an internal combustion engine, valve stems and guides will scuff and wear excessively if they are not adequately lubricated. Conversely, too much oil produces a heavy build up of deposits that can eventually cause significant engine problems. Valve stem seals are used to control the amount of oil allowed between a valve stem and a valve stem guide.
In the assembly of a valve system for an engine, it is important that the valve stem fit within an allowable tolerance in the valve stem guide. The valve stem seal is typically provided on the upper end of the valve stem to minimize the amount of oil that runs down the valve stem into the cylinder bore. A valve stem seal generally includes a sleeve designed to secure the seal to a valve stem guide. The inside diameter of the sleeve interfaces with and engages the outside diameter of the guide. The sleeve usually includes a sealing element that is centered about the valve stem to meter the oil that lubricates the inner diameter valve stem interface.
To a significant extent, the effectiveness of the valve stem seal depends on the manner to which the seal is secured to the guide. If the sleeve is not properly positioned in relation to the valve guide, the sealing element might not properly seat upon the valve stem, causing non-uniform contact pressure at the valve stem, undesirable wear patterns on the components, and unpredictable oil control for the valve stem.
Two-component valve stem seals having an inner resilient member and an outer rigid member (and, optionally, a reinforcing spring) are known in the industry. Such conventional seals usually consist of an inner rubber material that is covered by a separately formed outer metal or ceramic material. Because the inner and outer components are formed separately in different manufacturing phases, additional processing techniques or steps are often required to durably connect and/or bond the components to one another. There are a number of disadvantages associated with forming a two-component seal in such a manner. In addition to increasing the chance for misalignment and a poor fit between the inner and outer components, such additional processing techniques or steps may involve supplementary manufacturing techniques, production equipment and tooling, thereby increasing the costs associated with the production of an acceptable valve stem seal assembly.